


Experiment

by Chexmixup



Category: Ensemble Stars! (Video Game)
Genre: Angst, Explicit Sex, First year Natsume, M/M, ReiRitsu but ritsu isn't in it, Second Year Rei, Second year Wataru, it's definitely more than implied tho, plot with porn in it?, takes place a year before canon
Language: English
Status: Completed
Published: 2018-09-26
Updated: 2018-09-26
Packaged: 2019-07-18 01:02:20
Rating: Explicit
Warnings: Underage
Chapters: 1
Words: 3,901
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16107512
Author URL: https://archiveofourown.org/users/Chexmixup/pseuds/Chexmixup
Summary: Natsume finds himself more and more intrigued after a questionable encounter with Rei.





	Experiment

**Author's Note:**

> i apologize now for this headcanon heavy piece of shit. id also like to thank my good friends in trickstarpiss support group and my lovely girlfriend for helping me come up with something so awful. i honestly didnt even intend to post this shit, i wrote it for my friends just to see it flesh out in writing but my girlfriend insisted i post it so i did
> 
> please read the tags yall so you know what youre getting into

Natsume squeezed his eyes shut, arching his back in a drawn out moan. He dragged his nails down Rei’s back and relished in the way Rei groaned into his ear. “N-niisan!” He let’s the name slip in a breathy sigh but can’t be bothered to be embarrassed as he feels Rei slam into him harder. He lets out a choked moan and chants the name again, feeling the grasp on his rational thinking slipping further out of reach.

 

“Call me Onii-chan,” Rei pants, pounding into Natsume at a staccato pace, leaving the redhead breathless in his wanton noises.

 

“Onii-chan, o-oh-onii-chan!” Natsume shouts, grinding his hips down against Rei. This draws a moan from the older, and he leans down to brush his fangs against Natsume’s neck. He chuckled in that low, seductive voice when Natsume bares his neck for the other.

 

“You’re doing so good for onii-chan, you feel so  _ good _ ~” He praised before nipping slightly-  _ unsatisfyingly _ \- at Natsume’s neck, breathing in deeply as he fucked into the younger. “Do you wanna cum with onii-chan inside you?” He moved the hand that was gripping his hip, trailing it lazily along his hips.

 

“Yes,” Natsume breathed, arching his hips as his cock ached for those fingers to inch just a  _ little _ to the left.

 

“Hmm, what was that?” Rei taunted, slowing his pace and leaving his fingers to idly trace his hip bones.

 

“Yes, onii-chan yes!” Begged Natsume, crying out when he felt Rei slam his hips forward as his fingers finally grasped the redhead’s dick, pumping him rapidly. Natsume bit his lip to try and keep his voice in check, but Rei was hitting somewhere inside him  _ perfectly _ and it was so difficult.

 

“Mmh, now this won’t do. Let me hear that beautiful voice.” Natsume could feel Rei’s hot breath against his ear, the words vibrating against him and he wouldn’t argue with Rei, he  _ couldn’t _ . He let out a loud gasp, trying to both roll his hips up into his hand while grinding down to get Rei’s cock deeper inside him. “That’s it, just like that~ Cum for onii-chan, Ritsu.”

 

Natsume felt everything inside him  _ snap _ , his eyes opening as he bucked his hips up and came with a loud cry. His mind went blank, his body tensing as he felt a rush of ecstasy crash into him. He’s dimly aware of Rei’s thrusting, losing his pace and becoming frantic as he reached his climax. He could feel Rei spilling into the condom, rolling his hips sluggishly for a while longer, though his mind could hardly connect him to what he was feeling. It took a few moments yet for Natsume to come to himself, feeling his head clear as he stared up at the ceiling, gasping in deeply.

 

Rei had called Ritsu’s name. During sex. Rei was having sex with him, but he called _Ritsu’s_ name. As if Rei was picturing Ritsu instead of Natsume. Rei- did he- _did_ _he want Ritsu??_ Why was he with Natsume then, it wasn’t as if the redhead was the one to initiate. Oh god- _Did he settle for Natsume???_

 

Something about the thought made Natsume’s stomach churn, feeling a pressure on his chest that had nothing to do with the way Rei was leaning into him. Natsume was a replacement for what Rei had really wanted; it wasn’t as if they had something together, nor did Natsume have a reason to really feel upset. Rei had wanted sex, that was what it was, and he just happened to be the one available.

 

It was an intoxicating spiral of thoughts, his cooling skin growing hotter the more he lost himself. It had something to do with the way he felt  _ wrong _ ,  _ used _ by someone he looked up to so much. He shook himself before he could focus too much further, pushing Rei off of him with a reluctant groan and a smirk.

 

“This has been Fun, Rei-niisan. But really, I should get Going.” He pulled himself into a sitting position, grimacing at the soreness but not bothering to wait for the ache to subside as he got off of the clubroom table to redress. He didn’t spare a glance backwards, despite feeling Rei’s questioning stare. He threw his uniform on haphazardly, rushing to fix his hair. “I’ll talk to you after Class,” He said hurriedly, leaving the room without waiting to hear anything back from the elder Sakuma. As soon as he closed the door, he took a deep breath, steeling himself long enough to make it to the bathroom. He did what he could to calm his racing heart: splashing water on his face, smacking his cheek when that hadn’t worked, and gripping the sink when that did even less.

 

Rei called Ritsu’s name, and it was  _ bothering _ Natsume, in the worst and best of ways. He felt disgusted with himself, yet he couldn’t deny that it was deliriously pleasing to think that his senpai was using him. 

 

There was something wrong with him; clearly no one in a healthy mindset would crave the feeling of being used. Natsume didn’t care to really think why that might be, instead reveling in the rush of excitement that pleasing his senpais in whatever way he could brought. He could care less what his reasoning may be, for the moment he relished in the feeling of his blood thrumming with anticipation. He was going to try it again.

 

___

 

It was no secret that there was something going on between the Sakuma brothers, especially from the other eccentrics that Rei considered his closest friends. The eldest was known for his devotion to his little brother, even before he’d revealed his “little secret”. Natsume wasn’t stupid in thinking he came before the younger Sakuma, had never wanted to. He was perfectly content with being in Rei’s inner circle, which was about as close to Rei as he truly wanted to be. But something had  _ changed _ when Rei called Ritsu’s name. Not only did it solidify the truth that even if Rei wasn’t fucking his younger brother, her certainly wanted to; but it brought to life the idea that Rei was willing to use people- specifically Natsume- to get off on his little fantasy. And that made Natsume want to get closer to the confusing mess, see how long it might take before he breaks down, completely used and discarded.

 

Wow, there was a  _ lot _ to unpack, but for the time being Natsume figured it could wait until he was much older, telling his life story to some two-bit therapist in the city. Instead he continued to see Rei, now  _ always _ being the one to initiate, but never the one to finish first. At first maybe it was just curiosity, but it fleshed out into a sick fantasy of his own.

 

It wasn’t every time, as far as Natsume had noticed. There were times that Natsume was acknowledged, or times that Rei was just disconnected entirely. Natsume was performing an experiment, he didn’t care for the intimacy that occasionally bled into their rendezvous. If the kissing wasn’t bruising and bloody, he didn’t want it; he didn’t want to hear his name murmured softly, as if it were something  _ cherished _ . He had something to prove! It just so happened to get him off, which further drove his testing.

 

He learned that calling Rei “onii-chan” was what normally pushed the elder into his little fantasy world. Once he knew the secret, their get-togethers  _ always _ hit the spot in a way that chipped and cracked at his psyche.

 

But Natsume wanted to branch out. His thirst for the vampire had been quenched- to an extent, he was  _ always _ available if Rei called- so he decided to test it with someone else, specifically, another senpai.

 

That’s how he found himself in Wataru’s lap, fingers carding through his silken hair as his former mentor’s lips brushed against his pulse. He hummed, rolling down his hips to try and get his senior to bite down. Instead he heard a breathy chuckle before he felt teeth graze his porcelain skin.

 

“Natsume, you seem eager.”

 

Something felt wrong about hearing his name called, it wasn’t what he was here for. He’d have to change that as soon as possible; he wasn’t having sex to be praised nor to make himself feel better, and the sooner Wataru stopped the intimacy, the better.

 

“Mmm, Wataru-niisan, I’m here for something Interesting,” He said as seductively as he could manager, leaning up to whisper against his mentor’s ear before slightly tracing his tongue around its shell. He felt the other shiver and lean in closer to the redhead, causing him to smirk slightly. “Maybe I could blindfold You? Or perhaps,” Natsume hesitated for a moment further, but swallowed his pride. He was this far in, he couldn’t back down. If it was anything like his previous experience, the magician wouldn’t even notice the intention. “Perhaps we could Role-play?”

 

He felt his senpai perk up at that, cocking his head slightly to cast an amused gaze at the redhead. “What sort of role-play might that be?” He drawled, leaning close enough to tease his lips against Natsume’s, who pulled away before they could kiss. He really,  _ really _ wasn’t craving that sort of intimacy.

 

“Is there anything you’ve wanted to Try?” He pauses, taking a deep breath. “Anyone you’ve ever wanted to be With?” A little on the nose, but oh well, there was no use lamenting in what’s already been said.

 

“Hmm~?” Wataru pulled back a little further, his eyes narrowing in what Natsume hoped to be thought before he shrugged with his ever interested grin. “Now why would I want to be with anyone else when I have my extravagant student in my lap~?” Despite all the effort he’d put into keeping up with his facade, Natsume couldn’t help the pout that crossed his face. In  _ any _ circumstance he’d hate to seem like an immature child to anyone, let alone his senpais- this was absolutely mortifying. But Natsume couldn’t help it! He was disappointed! That didn’t mean he wasn’t going to try, he just had to change his attack plan!

 

He quickly schools in his features, presenting the seductive expression he had tried before. But Wataru’s much too fast for him, and a lot smarter than he’d anticipated. He catches the look of disappointment and raises an eyebrow, sitting back away from Natsume.

 

“Tell me, what’s going on?” His voice had lost it’s tempting timbre, instead speaking plainly as he addressed the younger.

 

“I’m not sure what you’re talking about, Shishou,” Natsume uses the cherished title to his advantage, hoping to distract the other but it all seems for not. There’s this infuriating look of concern on his face, and Natsume’s frustration only heightens when he’s removed from the elder’s lap.

 

“As enticing as it would be to create a fantasy with you during the throes of passion, I can’t help but feel as though there’s something you’re hiding from me,” Wataru says this with a gentle smile, but Natsume can feel that keen stare on him as if seeing through him entirely.

 

“Now, Shishou, don’t think of me as so Conniving,” Natsume tries once again to brush aside his concern, smiling effortlessly in hopes of charming the other into submission. “I’m not the only one to play this Game. Rei-niisan enjoys it just as Thoroughly.” Something slams into Natsume as soon as the admission leaves him; he knows before it’s said that his innocuous confession will be taken as anything but. Wataru was always too adept at reading others, and Natsume had openly made a fool of himself.

 

“Oh? And what sort of game does Rei enjoy, in particular. Don’t spare me a detail, I love a good story.” Wataru prys, though his smile grows tense.

 

“It’s just that, Shishou. A Game.” Natsume shrugs, shaking his head dismissively. “He enjoys role-playing, and taught me well that I enjoy it Too. Don’t tell me you’re Jealous.”

 

“Nothing of the sort! I just- ah,” Wataru paused, as if for a loss of words, but the first year knew better. If he had to guess, he would bet that the magician was trying to stay impassive, keeping up the facade as though he wasn’t as emotionally invested as his line of questioning was proving. “Just, what is it you role-play? I can’t pretend that it’s something entertaining, as say, a forbidden love between a vampire and something as innocent and untainted as yourself. But, please, tell me. I’m terribly interested now, I’m not sure I can focus on anything else until I know the truth.”

 

Damn him for being so persistent, Natsume really hadn’t wanted any of this. Though, maybe it was what he deserved, he was sort of using Wataru in the same way that Rei used him. The thought snapped what little pride he had left. The feeling welling up inside him was guilt now, and the younger couldn’t help but hang his head in shame. This experiment might have blurred his judgement, but Natsume wasn’t a bad person, he would never hurt the people he cared about.

 

“Shishou, I must Apologize,” Natsume murmured, unable to lift his gaze to the other. “I- something of an experiment I had has clouded my reasoning, I apologize for entangling you in This.”

 

“Natsume, you don’t-” Natsume raised his hand to stop Wataru from finishing, and the other thankfully silenced.

 

“If you must know, a little while ago, Rei-niisan and I were- well- Intimate,” The redhead coughed, feeling himself flush in embarrassment. This was the last thing to be embarrassed over, but he no longer had his pride to hide under. “He’d asked me to call him onii-chan, and proceeded to call me-” another disgruntled cough, clearing his throat. “-he called me Ritsu.” He gave a moment to let his words sink in before turning up to face his upperclassman, seeing an entirely void expression. Panic quickly filled the witch, and he waved his hands defensively. “It wasn’t bad, Though! I- I enjoyed the Game! Enough to do it multiple Times!”

 

“Multiple times, you say?” Wataru’s voice was low, but not in the seductive manner Natsume had been craving earlier. This was far more threatening, something the first year wasn’t sure he’d been capable of. Something in the tone pushed the redhead further into guilt, this time for exposing Rei’s crime, one that Natsume wasn’t sure he was committing.

 

“Don’t- don’t take it like That,” He laughed nervously, his expression all but pleading.

 

“What other way is there to take it?” The other stood to his full height. “Have you spoken to him about this?”

 

Natsume turned away once more, looking the part of a guilty child. “Not directly, no.” His voice had finally gone soft, knowing he’d lost this battle.

 

“Come then, I think it’s time we’ve talked about it.” Reluctantly, Natsume stood too, feeling as though he was being punished by an angry parent. Ah well, what did this ounce more of shame matter in the long run?

 

They made their way to the student council room, knowing that he’d be “diligently” working at this hour. And surely enough, he was seated at his desk, being pestered by Keito as the two announced their arrival with a subtle knock.

 

Rei looked up from his work, a devious grin filling his expression as he saw them. However, Natsume couldn’t return any sort of pleasantries, and he knew without looking up that Wataru was forcing whatever he could in the presence of company.

 

“If you don’t mind, Hasume, we have something to discuss with our dear president,” The magician says in a voice that is anything but his normal, silencing whatever the vice-president had to say in the matter. “If you could leave us be, you would have our deepest of gratitudes.”

 

Rei turned to the aforementioned, shooing him away with the same devilish smirk. “Ya’ heard them, Hasume. Get lost. I’ll deal with it later.”

 

With a disgruntled sigh and an accusing stare, Keito left, closing the door slowly behind him.

 

“And to what do I owe the pleasure?” Rei addressed them finally, but his current company wasn’t having it.

 

“What is it you and Natsume have been up to?” Wataru took a step forward, leaving the younger to stand still at the room’s edge.

 

“Hmm? Oh, don’t tell me you’re jealous or something,” Rei laughed, clearly not reading the mood, or rather not caring to.

 

“No, far from it, in fact.” Wataru continued to walk forward until his hands were pressed to Rei’s desk, towering over the other. “Why would I be jealous of what you’ve been putting Natsume through?”

 

“Haaah? Putting him through? Last time I checked, he liked it just as much as I did!”

 

“He liked it because he’s too fragile to know otherwise!” Wataru said with a laugh, as cold as it was unforgiving. However, Natsume felt something similar to anger bubble in him, and he took a step forward.

 

“I’m not Fragile! I did this to myself, and just look, I’m Fine!” He raised his voice defensively, gathering the attention of the older two.

 

“I wouldn’t call this  _ fine _ ,” Wataru scoffed, shaking his head. “I don’t know if you’re aware, but you’re asking people to  _ use _ you when you want ‘role-play’!”

 

“But I’m Fine!” Natsume continued to insist, glaring unfairly at Wataru. Really, he was just looking out for his underclassman, but his manner was only proving to provoke Natsume. “I’m not some  _ child _ that needs to be cared for and treated Gently! If Rei-niisan wants to use me, let Him!”

 

“Wait!” Rei called, stopping the bickering almost immediately. “Just wait. I’m not  _ using _ Natsume, he’s been the one to come onto me!”

 

“See!” Natsume shouted, pointing vaguely at the two. “I did this to Myself! There isn’t any need to accuse Rei-nissan! I did This! Blame Me!”

 

Wataru was silent afterwards, just for a moment as he steeled himself and took a calming breath. “Natsume, you cannot take the blame for Rei calling someone else’s name. Sure, you came onto him but  _ nothing _ you can do will make someone fantasize about another, unless they had already intended to. He used your willingness, and you simply sought him out to see further. You couldn’t have caused this.”   
  


It was Natsume’s turn to fall silent, once again hanging his head in defeat. “I- what?” Rei started this time, dumbfounded as he looked between the two. “Ya’ know, I’m really not following this anymore. What are you trying to say?”

 

“Let me spell it out for you: You keep calling your brother’s name when you have sex with Natsume, and now you’ve convinced him that it’s something others want. He came to me, asking me to call him by someone else’s name, as if I could do that with a guiltless conscience.” Rei’s expression clouded the more Wataru spoke, but he wasn’t finished. “That you could do this to anyone, let alone someone you consider your friend, appalls me.”   
  


“Natsume, is this true?” Rei’s voice was low as he addressed the younger, though not looking away from Wataru.

 

Natsume didn’t want to answer, wished he could remain silent and just leave this conversation between the two who seemed willing to discuss it. Actually, if he was wishing for things, he wished he hadn’t been found out. Maybe a small part of him wished he hadn’t gotten involved in this at all, that he found regular sex as appealing as the emotionally damaging kind. Instead, he bit his lip and nodded. “Yes, it’s true,” He murmured, just in case he hadn’t been seen.

 

“I’ve been callin’ you Ritsu this whole time?”  Natsume nodded, and Rei must be watching him now because he continued. “You never said anything to me?” He shook his head, not daring look at the other again. “Why?” Hearing the hurt in his voice, the first year trembled unintentionally.

 

“I liked the feeling,” He says hopelessly, further averting his gaze. “You didn’t seem to mind, and, after all you’ve done for me, I was glad to do what I could.” He stops, feeling his heart racing in his chest and his face flushing in heavy embarrassment, or rather shame. “I don’t know how much I really liked it, if I must confess. It makes me a little sick, but it isn’t my place to say. My nii-sans mean so much to me, you’ve all hurt for me. I can take it. I’m not- I’m not a fragile child…” Natsume trailed off, his hands fisting at his sides and his shoulders tensing. He was met with nothing but silence to answer his confession, which heightened his feelings of shame and insecurity. After a moment, he felt a warm hand resting on his back, looking up finally to find Wataru staring at him with the most gentle stares he’d seen. He hated it, but couldn’t find it in himself to look away or dismiss it.

 

“Natsume, do you really think we did all of this because we think you’re fragile?” When he didn’t respond, Wataru sighed. “We protect you because you’re the future of this academy. We do this so you can lead the next generation of students in the dazzling manner only you’re capable of. I, nor anyone else, I’m sure, doubts your ability to stand on your own. But we do this so you don’t have to; when the day comes when we can no longer protect ourselves, we want to be able to rely on you instead.”

 

The redhead felt his eyes sting as he turned away completely, facing the wall so neither of the two could see him shamefully rubbing tears from his eyes. He wasn’t sure he was able to process exactly what he was feeling, beyond an immense warmth that spread through his chest. But in this situation, he didn’t necessarily have the time nor the strength to sort through any lingering thoughts. He pushed them aside, and as soon as he was sure there were no longer tears stubbornly filling his eyes, he turned to face them.

 

He realized Rei was no longer standing at his desk, but instead looming over Natsume in an intimidating manner. However, without even a moment to fret, the redhead was pulled into a tight grip, losing his balance and falling into Rei’s embrace. “You’re too damn smart to act this stupid, okay?” He said softly, Natsume fighting off the blush of embarrassment and rush of affection for the other. “I never wanted to use you, alright? If anyone’s the idiot, it’s me. So don’t play along with it.” He pulled away as his tone livened up, but his hands rested firmly on Natsume’s shoulders. “You’re stubborn as all hell, fight me next time! I won’t forgive ya’ if you don’t.” There was a soft smile gracing his features, despite the guilt-ridden look he was giving the younger. Natsume found himself nodding slowly, unsure of how to accept affection from his upperclassman. He hadn’t expected that getting found out would turn out so positively; instead of getting scolded- or worse, finding out he was nothing but some tagalong child that they hadn’t any interest in- he was being forced to realize he was cherished by his upperclassmen. This feeling was entirely different but something he welcomed; nothing to test and research, just trusted as is. 

**Author's Note:**

> i hope you enjoyed this mistake. as always you can scream at me at any hour of the day, my dms are always open
> 
> main twitter: diklord9000  
> horny twitter: chexmistake


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